#include <fstream>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
const int N=5000000;
int v[N];
int d[N];
int main()
{
    int st,dr,i,n,k;
    long long s=0;
    in>>n>>k;
    st=0;
    dr=-1;
    for(int i=0 ; i<n ; i++)
    {
        in>>v[i];
        if(st<=dr && d[st]==i-k)
        {
             st++;
        }
        while(st<=dr && v[i]<=v[d[dr]])
        {
             dr--;
        }
        d[++dr]=i;
        if(i>=k-1)
        {
            s+=v[d[st]];
        }
    }
    out<<s;
    return 0;
}